Lapping machine



Jan.17, 1961 Filed April '7, 1958 2 Sheets-Sheet 1 i I 423 if 56 56- v|'h 1- l 2 70 66 Il 278. .62 l1 70 A J" I I "l: l' 56" 85. '71 36 35f--45 v /M n @a N -51 ill 32 j? 18 2 kLg L66 f 761 j! Q'. Ze 85 @0 /686% INVENTORS.

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United States Patent LAPPING MACHINE Stephen A. Boettcher, Evanston, andJack C. Page, Palatine, Ill., assignors to YAbrading Systems Company,Skokie, Ill., a corporation of Illinois Filed Apr. 7, 1958, Ser. No.726,753

7 Claims. (Cl. 51129) This invention relates to lapping machines andparticularly to improvements in machines for lapping fiat and parallelsurfaces on machined, ground, or precisioncast work pieces. In general,such machines comprise a horizontal lapping wheel or plate which isrotated about a vertical axis and which has an annular lapping surfaceon which the Work pieces are placed, in confined positions, so thatmovement of the lap surface relative to the work pieces brings aboutabrasive wear of the latter at their surfaces in engagement with saidlapping surface. Of paramount importance in all such machines of thisclass is the maintenance of the lapping surface in planar condition. Itis well known that the lapping sur face of the wheel tends to wearunevenly in the lapping operation, which, if not corrected, renders thelapping wheel ineffective for its intended usage.

The present invention is particularly directed to an improved means formaintaining the lapping surface corrected to a true planar condition andfor accomplishing such function substantially simultaneously with thelapping operation which creates the need for the correction.

In brief, a lapping machine embodying this invention may comprise adrum-like base or pedestal at the upper end of which is supported ahorizontal lapping wheel rotatable about a vertical axis. A horizontalstaging table surrounds the lapping wheel to provide an area foraccommodating Work pieces as the same are fed to and taken from thelapping wheel. A bridge structure is provided over the lapping wheel,carrying a plurality of vertical spindles, each of which, at its lowerend, centers a circular weight plate resting on work pieces on thewheel, such weight plate, in turn, loosely centering a surroundingretaining ring also resting on the wheel. As the wheel rotates, so dothe rings on their own axes, and so do the weight plates (by way of thework pieces); the retaining rings are truing elements for the lappingsurface, the combined wear effect of the bottoms of the rings and thework pieces beneath the weight plates being relied upon to maintain thesurface of the lapping wheel in a planar condition. The spindles arefixed, but are vertically adjustable for the purpose of applyingVpressure to the work pieces in addition to the weight of the weightplates. Importantly, the present invention provides braking means forcontrolling the rotational velocity of the retaining rings and the groupof work pieces on the lap, the braking means, in the form shown, beinginterposed between the fixed spindle and the weight plate and beingadjustable for varying the amount of its brak ing effect, thus tocontrol the wear effect of the work pieces and the ring on the lappingwheel.

Figure 1 is an elevation, with parts shown in crosssection, of the upperportions of a lapping machine vembodyingthe improvements of thisinvention.

Figure 2 is a partial cross-sectional View, on a larger scale, takensubstantially on line 2 2 of Figure 1, looking in the direction of thearrows;

Figure 3 is a partial plan view on the line 3-3 of Figure l; and

Figure 4 is a view on the line 4-4 of Figure 2, looking downwardly.

The machine villustrated has a cylindrical supporting pedestal 11 havinga door 14 for access to the interior.-

AS seen in Figure l, cylindrical collar 17 is mounted in the upper endof pedestal 11 by means of an inclined drip pan 18 for receiving, forreturn, abrasive and carrier mixture used in the lapping operation.

A motor mount 25 pivotally carried on a verticalaxle 26 is positionedwithin pedestal 11 for carrying a main drive electric motor 27. Sheavewheel and belt drive means 28 serve to interconnect motor 27 with a.lconventional gear reducer unit 30, mounted within ring;

17 and held to an internal flange 17 on the said ring by bolts 31, 31.Output shaft 32 of the gear reducer unit is keyed or otherwise affixedto a hub portion 33 of ro-` tatable lapping wheel 35.

As best shown by Figures 3 and 4, lapping wheel 35 comprises a circularwear resisting metallic alloy disc` having a central depression or wellbore 36, thus defining an annular lapping surface 40. A plurality ofradial sots 41, 41 are cut in the wheel to the depth of the center wellbore, according to conventional practice, which slots receive and carryaway abrasive and oil mixture, fed to the lapping wheel from a dripsupply line 43.

Surrounding the lapping wheel 35 is a ring 44 on which is mounted aplanar staging table 45. Said table45 hasV The lower end of each spindleis fitted into a ballY bearing 65 (Fig. 2) mounted in a shouldered wellbore 66 formed into the upper face of the related Weight plate 68 ofdz'sc formation.

Each weight plate is surrounded with slight clearance, by atruing-retainer ring 70. The periphery of the Weight plate and theinside surface of the ring 70 can be knurled.

Work pieces, indicated at 71, are positioned freely on theY lappingwheel within the confines of ring 70 for retention in the circular areadefined thereby. There may, of course, be but one work piece.

In operation, as the lapping wheel rotates on its vertical axis, drivenby the motor 27, the ring 70 and the weight plate 68 (the latter by wayof the Work pieces 71) are made to rotate on their Vertical axes, asindicated by the arrows in Figure 3, abrasive and carrier mixture be-Ying fed thereto from the drip spout 43, the action resulting in theVlapping of the under surfaces of the workV pieces and the simultaneousdressing of the annular lap-` ping surface of the wheel 35. t

It is, of course, known that the pressure applied to the interfacialcontact between the rings or the work pieces, on the one hand, and thelapping surface, on the other, is a factor in the wear of the lappingsurface.

Relative movement between the twocontacting-surfaces' is also a factor,and that assumes particular importance here because of thecharacteristic arrangement fof.y the truing retainer rings and the groupof work pieces-confined therein and the weight plate on theannular-lapping surface; each such assembly lies entirely to one" sideof the axis of the lapping wheel, and the rings and their APatented Jan.17, 1961vr contents rotate about their axes in the same direction aS thelapping wheel rotates about its axis, clockwise or counter-clockwise asthe case, may be; the result is that, at the periphery of the lappingannulus, the ring assembly moves in the same direction as the lappingannulus, and that, centrally, the ring, assembly moves oppositely to thelapping annulus; We have discovered that, the lapping wheel rotating ata constant velocity, if means is provided to retard the ensuing rotationof Ithat assembly and making such means adjustable, such means enableseffective selection of the area of wear of the annular lapping surface;the wear is normally to concavity of the lapping surface, and if therotation of the assembly is retarded, the wear approaching the peripherywill'be increased, thus counteracting the tendency to concavity andmaintaining the desired planar condition of the lapping surface. If thetendency should then be toward convexity, that can be met by permittinga speeding-up of the assembly.

As previously stated, we provide a braking means interposed between eachof the fixed spindles and its related weight plate, adjustable forvarying its braking effect, to regulate the rotational velocities of theweight plate and the truing-retainer ring and the wear effect of thework pieces and the ring on the lapping wheel.

We apply the braking means to the weight plate as indicated at 62 inFigure 1 and as shown in detail in Figures 3 and 4. The constructionembodies a plurality of friction disc elements 75 which are keyed to thespindle 56, as by mating key projections 76 and a vertical keyway in thespindle 56. Alternating with the friction disc elements 75 are brakeplates 78 which fit freely about the spindle 56 so that they arerotatable with respect thereto. Plates 78 are of a larger diameter thanthe disc elements 75, and` are attached to the weight plate 68, as bystud bolt 80 received in the threaded opening 81 in the weight plate. Aclamping cap 82, having threading engagement with threads 83 on thespindle 56, engages the uppermost of the disc elements 75, with a springwasher 84 intervening. An annular recess 86 in cap 82 accommodates theheads of the bolts 80. By threading the clamping cap 82 on the threads83, said cap being knurled at S7, variations in the braking effect ofthe brake members 75 and 78 may be had inorder to retard or free therotation of the weight plates 68 andthe related wear rings.

A protecting shroud ring 85, fitted into annular slot 86 in the weightplate 68, surrounds the several friction discs and plates 75 and 78.

In routine, the rings 70 are on the staging table and the work piecesare disposed therein, such assembly being then moved onto the lappingannulus to position where the spindle 56, braking means 62 and weightplate 68 are lowered into the ring and onto the work pieces and presseddownwardly to the desired pressure, then tightening the set screws 60.Periodically, the plane of the lapping surface may be checked; and, ifconcavity appears, the knurled clamping cap 82 is manipulated tocounteract it. When that particular lapping operation is Completed, theset-screws 6l) are released, the spindles, braking means and weightplates are lifted out of their rings, and the rings, still containingthe work pieces are` moved onto the staging table for removal from themachine.

We claim:

l. In a lapping machine, a rotatably operated lap having a planarlapping surface, truing means frictionally engaging said surface andthereby being rotatably driven about a fixed axis transverse to saidsurface, and means acting laterally against said truing means foradjustably retarding rotational velocity of said truing meansindependently of downward pressure on said lapping surface to regulateabrasive wear of said surface.

2. In a lapping machine, an operating lap having a planar, annularlapping surface, a truing ring engaging4 said lapping surface androtating relative thereto, fixed spindle means and a circular weightplate within said ring defining the rotational axis for said ring, andmeans including a friction brake means on said spindle means, toselectively adjust rotational velocity of said ring independently ofdownward pressure on said lapping surface, thereby to control Wear ofsaid lapping surface.

3. In a lapping machine, a rotatable lapping element having a planarlapping surface, said lapping element comprising a wheel rotatable on avertical axis, retaining and truing ring means engaging said lappingsurface on one side of said axis, said ring means being restrained torotate about a vertical axis and being frictionally driven by said lap,and brake means acting laterally against said ring means for regulatingthe rotational velocity of said ring means independently of downwardpressure on said lapping surface, thereby to control the velocitythereof relative to said lapping surface for the purpose of maintainingthe latter in planar condition.

4. In a lapping machine, a disc rotatable on a vertical axis and havinga horizontal annular planar lapping surface, retaining and truing ringmeans resting across said surface, a weight plate within each ring meanswith close clearance and adapted to rest on work pieces confined in saidrings and resting on said lapping surface, vertical spindle meansdefining fixed rotational axes for said weight plate and ring means, andmeans for selectively regulating the rotational velocity of said weightplate and ring means independently of downward pressure on said lappingsurface to selectively regulate wear of said lapping means to maintainthe same in planar condition.

5. In a lapping machine, a disc rotatable on a vertical axis and havinga planar lapping surface, a retaining and truing ring resting on saidlapping surface, a weight plate in said ring and adapted to rest ongrouped work pieces confined within said ring and resting on saidlapping surface, fixed axis means centering said plate and ring so thatthey are rotatably driven by frictional engagement with said lappingsurface, and means independent of downward pressure on said lappingsurface for selectively braking the rotation of said weight plate, ringand work-piece group to regulate wear of said lapping surface.

6. In a lapping machine, a disc rotatable on a vertical axis and havinga planar lapping surface, a retaining and truing ring resting on saidlapping surface to one side of said vertical axis, a weight platedisposed with slight clearance in said ring and adapted to rest on workpieces resting on said lapping surface within said ring, a verticalspindle centering said weight plate and being vertically adjustable toregulate downward pressure on said weight plate, and adjustable brakingmeans interposed between said spindle and said weight plate to regulatethe rotational velocity of said weight plate, said braking meanscomprising a set of friction discs keyed to said spindle and a set ofalternate friction discs fixed to said Weight plate to rotate therewith,and means for adjustably clamping said sets of friction discs together.

7. In a lapping machine, a disc rotatable on a vertical axis and havinga planar lapping surface, a retaining and truing ring resting on saidlapping surface on one side of said axis, said ring being held on itsown fixed axis and being rotatable thereon by its frictional engagementwith said lapping surface, and means acting laterally against said ringfor adjustably braking its said rotation.

References Cited in the file of this patent UNITED STATES PATENTS TJUA

